Known in a prior art is a rotary vane type compressor which includes a rotor arranged in a cylindrical housing having a predetermined inner surface profile, through which rotor vane plates, having a length larger than the diameter of the rotor, are slidably inserted, so that vane plates always contact, at their ends, the inner profile of the housing during the rotation of the rotor. Compressor chambers are thus formed between the vane plates, the rotor and the housing. A cooling medium is sucked into the chambers and forced from the chamber during each rotation of the rotor. The rotor has at its ends cylindrical seal portions and shaft portions adjacent to the cylindrical seal portions. The cylindrical seal portions are inserted in the respective cylindrical recesses formed in side plates, so that annular slits or clearances of very small thickness are formed between the side plates and the cylindrical seal portions. The shaft portions are supported on the side plates by means of bearing units, arranged in bearing chambers formed between the housing and the rotor. The bearing chambers are opened to the respective annular slits.
The rotor effects a high speed sliding motion with respect to the inner surface of the cylindrical housing. Thus, in order to lubricate the parts of the compressor, a means is provided for supplying the lubrication oil into the compression chambers. The oil supplied to the compression chambers leaks into the bearing chamber via the annular slits to lubricate the bearing units.
The prior art compressor suffers from a drawback in that parts comprising the compressor are apt to be destroyed due to the large force applied thereto when the compressor is started. This large force is generated by an accumulation of oil in the compression chambers on the one hand and by a pressure difference occuring between the bearing chambers on the other hand. The accumulation of oil in the compression chambers occurs because no provision is made to close the chambers in the oil supply conduit in the prior art. An extremely large pressure is generated in the chamber due to a fluid compression when starting the compressor which causes the generation of a large force, sufficient to destroy parts of compressor.
The pressure difference is caused by the independent structure of the bearing chambers in the prior art. The pressure difference becomes large when the compressor is started in a cold state under a non-equalized accumulation of oil in the bearing chambers. Due to the large pressure difference, a thrust force is applied to the rotor, causing wear of the vanes or side plates, or causing the thermal sticking of such parts. In order to overcome this drawback, a means may be provided for communicating the bearing chambers with the compression chambers, so that the pressure in the chambers is equalized. However, the leakage of the coolant medium from the compression chambers to the bearing chambers, or the leakage of oil from the bearing chambers to the compression chambers takes place due to the existence of the annular slits in the cylindrical seal portions of the rotor member. Due to such leakage, the compression efficiency is decreased.